This invention relates to a microelectromechanical or nanoelectromechanical resonator architecture or structure, and method of designing, operating, controlling and/or using such a resonator; and more particularly, in one aspect, to a microelectromechanical or nanoelectromechanical resonator architecture or structure having a ring-like shape wherein the resonator, when induced, resonates in primarily or substantially an elongating or breathing mode or motion.
Generally, high Q microelectromechanical resonators are regarded as a promising choice for integrated single chip frequency references and filter. In this regard, high Q microelectromechanical resonators tend to provide high frequency outputs that are suitable for many high frequency applications requiring compact and/or demanding space constrained designs. However, while the resonator is being scaled smaller, packaging stress, energy loss into the substrate through substrate anchors and/or reduced signal strength tend to adversely impact the frequency stability as well as “Q” of the resonator.
There are several well-known resonator architectures. For example, one group of conventional resonator architectures employs a closed-ended or an open-ended tuning fork. For example, a closed-ended or double-clamped tuning fork resonator includes beams or tines that are anchored to substrate via anchors. The tuning fork architecture employs fixed electrodes to induce a force to or on the beams/tines to cause or induce the beams/tines to oscillate (in-plane).
The characteristics and response of tuning fork resonators are well known. However, such resonator architectures are often susceptible to changes in mechanical frequency of resonator by inducing strain into resonator beams/tines as a result of packaging stress. In addition, such conventional resonator architectures typically experience or exhibit energy loss, through the anchors, into the substrate.
Moreover, the characteristics and response of such conventional resonators are highly susceptible and/or influenced by manufacturing tolerances of conventional manufacturing processes (for example, photolithography and/or etching processes). Accordingly, manufacturing conventional resonators having a precise resonant frequency, on a repeatable and predictable basis, is challenging.
Certain architectures and techniques have been described to address Q-limiting loss mechanism of energy loss into the substrate through anchors as well as changes in frequency due to certain stresses. In one embodiment, the beams of the resonator may be “suspended” above the ground plane and sense electrode whereby the vibration mode of the beam is out-of-plane. (See, for example, U.S. Pat. No. 6,249,073). While such architectures may alleviate energy loss through the anchors, resonators that include an out-of-plane vibration mode (i.e., transverse mode) tend to exhibit relatively large parasitic capacitance between drive/sense electrodes and the substrate. Such capacitance may lead to a higher noise floor of the output signal (in certain designs).
Other techniques designed to improve the Q-factor of the resonator have been proposed and include designing the spacing between the vibrating beams so that such beams are closely spaced relative to a wavelength associated with their vibrating frequency. (See, for example, the single-ended or single-clamped resonator of U.S. Pat. No. 6,624,726). The vibrating beams are driven to vibrate one-half of a vibration period out of phase with each other (i.e., to mirror each other's motion). While these architectures and techniques to improve the Q of the resonator may suppress acoustic energy leakage, such an architecture remains predisposed to packaging stress, energy loss into the substrate through substrate anchors as well as a “moving” of the center of gravity of the resonator during motion by the vibrating beams of the single-ended or single-clamped resonator.
Other resonator architectures have been described to address energy loss through the anchor, for example, a “disk” shaped resonator design. (See, for example, U.S. Patent Application Publication 2004/0207492 and U.S. Pat. No. 6,628,177). Yet another resonator architecture has been proposed that is a “hollow-disk” ring resonator design. (See “Micromechanical “Hollow-Disk” Ring Resonator”, Li et al., MEMS 2004 (IEEE), pages 821-825). In this design, it is stated that, among other things, the anchor technique employed therein suppresses energy loss through the anchor which allows the annular ring-type resonator to achieve a high Q.
Notably, as mentioned above, the characteristics and response of conventional resonators are highly susceptible and/or influenced by manufacturing tolerances of conventional fabrication processes (for example, photolithography and/or etching processes). As such, these tolerances and/or imperfections may have a dramatic impact on the resulting mechanical frequency of the resonator.
Thus, there is a need for a resonator architecture, configurations or structure, and method of designing, operating, controlling and/or using such a resonator that overcomes the shortcomings of one, some or all of the conventional microelectromechanical resonator architectures, configurations or structures. In this regard, there is a need for improved microelectromechanical and/or nanoelectromechanical resonators having improved packaging stress characteristics, reduced energy loss (i) into the substrate through substrate anchors and/or (ii) due to thermo elastic dissipation (TED), improved immunity to tolerances in the manufacturing processes (for example, photolithography and/or etching processes), and/or greater predictability and repeatability of the resonant frequency. In this way, the predictability, repeatability, stability and/or linearity of the output frequency of the resonator is enhanced and/or the “Q” factor of the resonator is relatively high.